JAPAN'S Prime Minister Naoto Kan said he had ordered the shutdown of a nuclear power plant southwest of Tokyo because it is located close to a dangerous tectonic faultline.

The news comes eight weeks after a massive quake and tsunami damaged the Fukushima Daiichi nuclear power plant northeast of Tokyo, sparking the world's worst atomic crisis since Chernobyl a quarter-century ago.

Seismologists have long warned that a major quake is long overdue in the Tokai region southwest of Tokyo where the Hamaoka plant is located, about 200km from Tokyo in Shizuoka prefecture.

"As prime minister, I have ordered, through trade minister (Banri) Kaieda, that Chubu Electric Power halt operations of all the reactors at the Hamaoka nuclear power plant," Kan said at a televised press conference today.

Two reactors, numbers four and five, are operating at Hamaoka.

"The relevant authorities, including the science ministry, have shown that the possibility of a magnitude-8.0 earthquake hitting the area of the Hamaoka plant within the next 30 years is 87 per cent," he said.

"This is a decision made for the safety of the people when I consider the special conditions of the Hamaoka plant."

Japanese anti-nuclear campaigners have long argued that the seismically unstable area, where two continental plates meet, makes the plant the most dangerous atomic facility in the country.